The invention relates to a circuit arrangement for a telephone station with ground connection to a central supply device for post-dialling signalling, where the telephone station utilizes a dialling and speech circuit with pulse circuit and a first polarity reversal protection device.
A central telephone exchange requires, for example, for post-dialling signals, (consultation etc.), a signalling mode which is in addition to the normal dialling information. It is dependent upon the central telephone exchange whether signalling must take place by a pulse (loop interruption) or by grounding the ungrounded terminal of the central supply device. Grounding or pulse are triggered by the same key. A circuit arrangement has already been proposed wherein the telephone station is automatically switched over to pulse function or ground signalling in dependence upon the central exchange. If a ground signal is required, ground is connected to the ground terminal point of the telephone station. If no ground is connected, a pulse function automatically exists. However, the circuit arrangement operates in the aforementioned manner only when, in the event that a ground signal is required, the positive terminal of the central supply device is grounded.